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	<p><a name="TOP"><b>Up:</b></a> <a
	href="http://www.qhull.org">Home page</a> for Qhull<br>
	<b>Up:</b><a
	href="http://www.qhull.org/news">News</a> about Qhull<br>
	<b>Up:</b> <a href="http://www.qhull.org/html/qh-faq.htm">FAQ</a> about Qhull<br>
	<b>To:</b> <a href="#TOC">Qhull manual: Table of Contents</a>
	(please wait while loading) <br>
	<b>To:</b> <a href="qh-quick.htm#programs">Programs</a>
	<a href="qh-quick.htm#options">Options</a>
	<a href="qh-opto.htm#output">Output</a>
	<a href="qh-optf.htm#format">Formats</a>
	<a href="qh-optg.htm#geomview">Geomview</a>
	<a href="qh-optp.htm#print">Print</a>
	<a href="qh-optq.htm#qhull">Qhull</a>
	<a href="qh-optc.htm#prec">Precision</a>
	<a href="qh-optt.htm#trace">Trace</a><br>

	<hr>
	<!-- Main text of document -->
	<h1><a
	href="http://www.geom.uiuc.edu/graphics/pix/Special_Topics/Computational_Geometry/fixed.html"><img
	src="qh--rand.gif" alt="[random-fixed]" align="middle"
	width="100" height="100"></a> Qhull manual </h1>

	<p>Qhull is a general dimension code for computing convex hulls,
	Delaunay triangulations, halfspace intersections about a point, Voronoi
	diagrams, furthest-site Delaunay triangulations, and
	furthest-site Voronoi diagrams. These structures have
	applications in science, engineering, statistics, and
	mathematics. See <a
	href="http://www.cs.mcgill.ca/~fukuda/soft/polyfaq/polyfaq.html">Fukuda's
	introduction</a> to convex hulls, Delaunay triangulations,
	Voronoi diagrams, and linear programming. For a detailed
	introduction, see O'Rourke [<a href="#orou94">'94</a>], <i>Computational
	Geometry in C</i>.
	</p>

	<p>There are six programs. Except for rbox, they use
	the same code. Each program includes instructions and examples.
	<blockquote>
	<ul>
	<li><a href="qconvex.htm">qconvex</a> -- convex hulls
	<li><a href="qdelaun.htm">qdelaunay</a> -- Delaunay triangulations and
	furthest-site Delaunay triangulations
	<li><a href="qhalf.htm">qhalf</a> -- halfspace intersections about a point
	<li><a href="qhull.htm">qhull</a> -- all structures with additional options
	<li><a href="qvoronoi.htm">qvoronoi</a> -- Voronoi diagrams and
	furthest-site Voronoi diagrams
	<li><a href="rbox.htm">rbox</a> -- generate point distributions for qhull
	</ul>
	</blockquote>

	<p>Qhull implements the Quickhull algorithm for computing the
	convex hull. Qhull includes options
	for hull volume, facet area, multiple output formats, and
	graphical output. It can approximate a convex hull. </p>

	<p>Qhull handles roundoff errors from floating point
	arithmetic. It generates a convex hull with "thick" facets.
	A facet's outer plane is clearly above all of the points;
	its inner plane is clearly below the facet's vertices. Any
	exact convex hull must lie between the inner and outer plane.

	<p>Qhull uses merged facets, triangulated output, or joggled
	input. Triangulated output triangulates non-simplicial, merged
	facets. Joggled input also
	guarantees simplicial output, but it
	is less accurate than merged facets. For merged facets, Qhull
	reports the maximum outer and inner plane.

	<p><i>Brad Barber, Arlington, MA</i></p>

	<p><b>Copyright © 1995-2015 C.B. Barber</b></p>

	<hr>

	<h2><a href="#TOP">»</a><a name="TOC">Qhull manual: Table of
	Contents </a></h2>

	<ul>
	<li><a href="#when">When</a> to use Qhull
	<ul>
	<li><a href="http://www.qhull.org/news">News</a> for Qhull
	with new features and reported bugs.
	<li><a href="http://www.qhull.org">Home</a> for Qhull with additional URLs
	(<a href=index.htm>local copy</a>)
	<li><a href="http://www.qhull.org/html/qh-faq.htm">FAQ</a> for Qhull (<a href="qh-faq.htm">local copy</a>)
	<li><a href="http://www.qhull.org/download">Download</a> Qhull (<a href=qh-get.htm>local copy</a>)
	<li><a href="qh-quick.htm#programs">Quick</a> reference for Qhull and its <a href="qh-quick.htm#options">options</a>
	<p>
	<li><a href="../COPYING.txt">COPYING.txt</a> - copyright notice<br>
	<li><a href="../REGISTER.txt">REGISTER.txt</a> - registration<br>
	<li><a href="../README.txt">README.txt</a> - installation
	instructions<br>
	<li><a href="../src/Changes.txt">Changes.txt</a> - change history <br>
	<li><a href="qhull.txt">qhull.txt</a> - Unix manual page
	</ul>
	<p>
	<li><a href="#description">Description</a> of Qhull
	<ul>
	<li><a href="#definition">de</a>finition <a
	href="#input">in</a>put <a href="#output">ou</a>tput
	<a href="#algorithm">al</a>gorithm <a
	href="#structure">da</a>ta structure </li>
	<li><a href="qh-impre.htm">Imprecision</a> in Qhull</li>
	<li><a href="qh-impre.htm#joggle">Merged facets</a> or joggled input
	<li><a href="qh-eg.htm">Examples</a> of Qhull</li>
	</ul>
	<p>
	<li><a href=qh-quick.htm#programs>Qhull programs</a>, with instructions and examples
	<ul>
	<li><a href="qconvex.htm">qconvex</a> -- convex hulls
	<li><a href="qdelaun.htm">qdelaunay</a> -- Delaunay triangulations and
	furthest-site Delaunay triangulations
	<li><a href="qhalf.htm">qhalf</a> -- halfspace intersections about a point
	<li><a href="qhull.htm">qhull</a> -- all structures with additional options
	<li><a href="qvoronoi.htm">qvoronoi</a> -- Voronoi diagrams and
	furthest-site Voronoi diagrams
	<li><a href="rbox.htm">rbox</a> -- generate point distributions for qhull
	</ul>
	<p>
	<li><a href="qh-quick.htm#options">Qhull options</a><ul>
	<li><a href="qh-opto.htm#output">Output</a> formats</li>
	<li><a href="qh-optf.htm#format">Additional</a> I/O
	formats</li>
	<li><a href="qh-optg.htm#geomview">Geomview</a>
	output options</li>
	<li><a href="qh-optp.htm#print">Print</a> options</li>
	<li><a href="qh-optq.htm#qhull">Qhull</a> control
	options</li>
	<li><a href="qh-optc.htm#prec">Precision</a> options</li>
	<li><a href="qh-optt.htm#trace">Trace</a> options</li>
	</ul>
	</li>
	<p>
	<li><a href="#geomview">Geomview</a>, Qhull's graphical viewer</li>
	<ul>
	<li><a href="#geomview-install">Installing Geomview</a></li>
	<li><a href="#geomview-use">Using Geomview</a></li>
	<li><a href="#geomview-win">Building Geomview for Windows</a></li>
	</ul>
	<p>
	<li><a href="qh-code.htm">Qhull internals</a><ul>
	<li><a href="qh-code.htm#reentrant">Reentrant</a> Qhull</li>
	<li><a href="qh-code.htm#64bit">Qhull</a> on 64-bit computers</li>
	<li><a href="qh-code.htm#cpp">Calling</a> Qhull
	from C++ programs</li>
	<li><a href="qh-code.htm#library">Calling</a> Qhull
	from C programs</li>
	<li><a href="qh-code.htm#performance">Performance</a>
	of Qhull</li>
	<li><a href="qh-code.htm#enhance">Enhancements</a> to
	Qhull</li>
	<li><a href="../src/libqhull_r/index.htm">Reentrant</a> Qhull functions, macros, and
	data structures </li>
	<li><a href="../src/libqhull/index.htm">Qhull</a> functions, macros, and
	data structures </li>
	</ul>
	</li>
	<p>
	<li>Related URLs
	<ul>

	<li><a href="news:comp.graphics.algorithms">Newsgroup</a>:
	comp.graphics.algorithms
	<li><a
	href="http://exaflop.org/docs/cgafaq/">FAQ</a> for computer graphics algorithms and
	<a href="http://exaflop.org/docs/cgafaq/cga6.html">geometric</a> structures.
	<li>Amenta's <a href="http://www.geom.uiuc.edu/software/cglist">Directory
	of Computational Geometry Software </a></li>
	<li>Erickson's <a
	href="http://compgeom.cs.uiuc.edu/~jeffe/compgeom/code.html">Computational
	Geometry Software</a> </li>
	<li>Fukuda's <a
	href="http://www.cs.mcgill.ca/~fukuda/soft/polyfaq/polyfaq.html">
	introduction</a> to convex hulls, Delaunay triangulations,
	Voronoi diagrams, and linear programming.
	<li>Stony Brook's <a
	href="http://www.cs.sunysb.edu/~algorith/major_section/1.6.shtml">Algorithm Repository</a> on computational geometry.
	</li>
	</ul>
	<p>
	<li><a href="#bugs">What to do</a> if something goes wrong</li>
	<li><a href="#email">Email</a></li>
	<li><a href="#authors">Authors</a></li>
	<li><a href="#ref">References</a></li>
	<li><a href="#acknowledge">Acknowledgments</a></li>
	</ul>
	<h2><a href="#TOC">»</a><a name="when">When to use Qhull</a></h2>
	<blockquote>

	<p>Qhull constructs convex hulls, Delaunay triangulations,
	halfspace intersections about a point, Voronoi diagrams, furthest-site Delaunay
	triangulations, and furthest-site Voronoi diagrams.</p>

	<p>For convex hulls and halfspace intersections, Qhull may be used
	for 2-d upto 8-d. For Voronoi diagrams and Delaunay triangulations, Qhull may be
	used for 2-d upto 7-d. In higher dimensions, the size of the output
	grows rapidly and Qhull does not work well with virtual memory.
	If <i>n</i> is the size of
	the input and <i>d</i> is the dimension (d>=3), the size of the output
	and execution time
	grows by <i>n^(floor(d/2)</i>
	[see <a href=qh-code.htm#performance>Performance</a>]. For example, do
	not try to build a 16-d convex hull of 1000 points. It will
	have on the order of 1,000,000,000,000,000,000,000,000 facets.

	<p>On a 600 MHz Pentium 3, Qhull computes the 2-d convex hull of
	300,000 cocircular points in 11 seconds. It computes the
	2-d Delaunay triangulation and 3-d convex hull of 120,000 points
	in 12 seconds. It computes the
	3-d Delaunay triangulation and 4-d convex hull of 40,000 points
	in 18 seconds. It computes the
	4-d Delaunay triangulation and 5-d convex hull of 6,000 points
	in 12 seconds. It computes the
	5-d Delaunay triangulation and 6-d convex hull of 1,000 points
	in 12 seconds. It computes the
	6-d Delaunay triangulation and 7-d convex hull of 300 points
	in 15 seconds. It computes the
	7-d Delaunay triangulation and 8-d convex hull of 120 points
	in 15 seconds. It computes the
	8-d Delaunay triangulation and 9-d convex hull of 70 points
	in 15 seconds. It computes the
	9-d Delaunay triangulation and 10-d convex hull of 50 points
	in 17 seconds. The 10-d convex hull of 50 points has about 90,000 facets.

	<!-- duplicated in index.htm and html/index.htm -->
	<p>Qhull does <i>not</i> support constrained Delaunay
	triangulations, triangulation of non-convex surfaces, mesh
	generation of non-convex objects, or medium-sized inputs in 9-D
	and higher. </p>

	<p>This is a big package with many options. It is one of the
	fastest available. It is the only 3-d code that handles precision
	problems due to floating point arithmetic. For example, it
	implements the identity function for extreme points (see <a
	href="qh-impre.htm">Imprecision in Qhull</a>). </p>

	<p>If you need a short code for convex hull, Delaunay
	triangulation, or Voronoi volumes consider Clarkson's <a
	href="http://www.netlib.org/voronoi/hull.html">hull
	program</a>. If you need 2-d Delaunay triangulations consider
	Shewchuk's <a href="http://www.cs.cmu.edu/~quake/triangle.html">triangle
	program</a>. It is much faster than Qhull and it allows
	constraints. Both programs use exact arithmetic. They are in <a
	href="http://www.netlib.org/voronoi/">http://www.netlib.org/voronoi/</a>.
	Qhull <a
	href="http://www.qhull.org/download">version
	1.0</a> may also meet your needs. It detects precision problems,
	but does not handle them.</p>

	<p><a href=http://www.algorithmic-solutions.com/enleda.htm>Leda</a> is a
	library for writing computational
	geometry programs and other combinatorial algorithms. It
	includes routines for computing 3-d convex
	hulls, 2-d Delaunay triangulations, and 3-d Delaunay triangulations.
	It provides rational arithmetic and graphical output. It runs on most
	platforms.

	<p>If your problem is in high dimensions with a few,
	non-simplicial facets, try Fukuda's <a
	href="http://www.cs.mcgill.ca/~fukuda/soft/cdd_home/cdd.html">cdd</a>.
	It is much faster than Qhull for these distributions. </p>

	<p>Custom software for 2-d and 3-d convex hulls may be faster
	than Qhull. Custom software should use less memory. Qhull uses
	general-dimension data structures and code. The data structures
	support non-simplicial facets.</p>

	<p>Qhull is not suitable for mesh generation or triangulation of
	arbitrary surfaces. You may use Qhull if the surface is convex or
	completely visible from an interior point (e.g., a star-shaped
	polyhedron). First, project each site to a sphere that is
	centered at the interior point. Then, compute the convex hull of
	the projected sites. The facets of the convex hull correspond to
	a triangulation of the surface. For mesh generation of arbitrary
	surfaces, see <a
	href="http://www-users.informatik.rwth-aachen.de/~roberts/meshgeneration.html">Schneiders'
	Finite Element Mesh Generation</a>.</p>

	<p>Qhull is not suitable for constrained Delaunay triangulations.
	With a lot of work, you can write a program that uses Qhull to
	add constraints by adding additional points to the triangulation.</p>

	<p>Qhull is not suitable for the subdivision of arbitrary
	objects. Use <tt>qdelaunay</tt> to subdivide a convex object.</p>

	</blockquote>
	<h2><a href="#TOC">»</a><a name="description">Description of
	Qhull </a></h2>
	<blockquote>

	<h3><a href="#TOC">»</a><a name="definition">definition</a></h3>
	<blockquote>

	<p>The <i>convex hull</i> of a point set <i>P</i> is the smallest
	convex set that contains <i>P</i>. If <i>P</i> is finite, the
	convex hull defines a matrix <i>A</i> and a vector <i>b</i> such
	that for all <i>x</i> in <i>P</i>, <i>Ax+b <= [0,...]</i>. </p>

	<p>Qhull computes the convex hull in 2-d, 3-d, 4-d, and higher
	dimensions. Qhull represents a convex hull as a list of facets.
	Each facet has a set of vertices, a set of neighboring facets,
	and a halfspace. A halfspace is defined by a unit normal and an
	offset (i.e., a row of <i>A</i> and an element of <i>b</i>). </p>

	<p>Qhull accounts for round-off error. It returns
	"thick" facets defined by two parallel hyperplanes. The
	outer planes contain all input points. The inner planes exclude
	all output vertices. See <a href="qh-impre.htm#imprecise">Imprecise
	convex hulls</a>.</p>

	<p>Qhull may be used for the Delaunay triangulation or the
	Voronoi diagram of a set of points. It may be used for the
	intersection of halfspaces. </p>

	</blockquote>
	<h3><a href="#TOC">»</a><a name="input">input format</a></h3>
	<blockquote>

	<p>The input data on <tt>stdin</tt> consists of:</p>

	<ul>
	<li>first line contains the dimension</li>
	<li>second line contains the number of input points</li>
	<li>remaining lines contain point coordinates</li>
	</ul>

	<p>For example: </p>

	<pre>
	3 #sample 3-d input
	5
	0.4 -0.5 1.0
	1000 -1e-5 -100
	0.3 0.2 0.1
	1.0 1.0 1.0
	0 0 0
	</pre>

	<p>Input may be entered by hand. End the input with a control-D
	(^D) character. </p>

	<p>To input data from a file, use I/O redirection or '<a
	href="qh-optt.htm#TI">TI file</a>'. The filename may not
	include spaces or quotes.</p>

	<p>A comment starts with a non-numeric character and continues to
	the end of line. The first comment is reported in summaries and
	statistics. With multiple <tt>qhull</tt> commands, use option '<a
	href="qh-optf.htm#FQ">FQ</a>' to place a comment in the output.</p>

	<p>The dimension and number of points can be reversed. Comments
	and line breaks are ignored. Error reporting is better if there
	is one point per line.</p>

	</blockquote>
	<h3><a href="#TOC">»</a><a name="option">option format</a></h3>
	<blockquote>

	<p>Use options to specify the output formats and control
	Qhull. The <tt>qhull</tt> program takes all options. The
	other programs use a subset of the options. They disallow
	experimental and inappropriate options.

	<blockquote>
	<ul>
	<li>
	qconvex == qhull
	<li>
	qdelaunay == qhull d Qbb
	<li>
	qhalf == qhull H
	<li>
	qvoronoi == qhull v Qbb
	</ul>
	</blockquote>

	<p>Single letters are used for output formats and precision
	constants. The other options are grouped into menus for formats
	('<a href="qh-optf.htm#format">F</a>'), Geomview ('<a
	href="qh-optg.htm#geomview">G </a>'), printing ('<a
	href="qh-optp.htm#print">P</a>'), Qhull control ('<a
	href="qh-optq.htm#qhull">Q </a>'), and tracing ('<a
	href="qh-optt.htm#trace">T</a>'). The menu options may be listed
	together (e.g., 'GrD3' for 'Gr' and 'GD3'). Options may be in any
	order. Capitalized options take a numeric argument (except for '<a
	href="qh-optp.htm#PG">PG</a>' and '<a href="qh-optf.htm#format">F</a>'
	options). Use option '<a href="qh-optf.htm#FO">FO</a>' to print
	the selected options.</p>

	<p>Qhull uses zero-relative indexing. If there are <i>n</i>
	points, the index of the first point is <i>0</i> and the index of
	the last point is <i>n-1</i>.</p>

	<p>The default options are:</p>

	<ul>
	<li>summary output ('<a href="qh-opto.htm#s">s</a>') </li>
	<li>merged facets ('<a href="qh-optc.htm#C0">C-0</a>' in 2-d,
	3-d, 4-d; '<a href="qh-optq.htm#Qx">Qx</a>' in 5-d and
	up)</li>
	</ul>

	<p>Except for bounding box
	('<a href="qh-optq.htm#Qbk">Qbk:n</a>', etc.), drop facets
	('<a href="qh-optp.htm#Pdk">Pdk:n</a>', etc.), and
	Qhull command ('<a href="qh-optf.htm#FQ">FQ</a>'), only the last
	occurence of an option counts.
	Bounding box and drop facets may be repeated for each dimension.
	Option 'FQ' may be repeated any number of times.

	<p>The Unix <tt>tcsh</tt> and <tt>ksh </tt>shells make it easy to
	try out different options. In Windows 95, use a command window with <tt>doskey</tt>
	and a window scroller (e.g., <tt>peruse</tt>). </p>

	</blockquote>
	<h3><a href="#TOC">»</a><a name="output">output format</a></h3>
	<blockquote>

	<p>To write the results to a file, use I/O redirection or '<a
	href="qh-optt.htm#TO">TO file</a>'. Windows 95 users should use
	'TO file' or the console. If a filename is surrounded by single quotes,
	it may include spaces.
	</p>

	<p>The default output option is a short summary ('<a
	href="qh-opto.htm#s">s</a>') to <tt>stdout</tt>. There are many
	others (see <a href="qh-opto.htm">output</a> and <a
	href="qh-optf.htm">formats</a>). You can list vertex incidences,
	vertices and facets, vertex coordinates, or facet normals. You
	can view Qhull objects with Geomview, Mathematica, or Maple. You can
	print the internal data structures. You can call Qhull from your
	application (see <a href="qh-code.htm#library">Qhull library</a>).</p>

	<p>For example, 'qhull <a href="qh-opto.htm#o">o</a>' lists the
	vertices and facets of the convex hull. </p>

	<p>Error messages and additional summaries ('<a
	href="qh-opto.htm#s">s</a>') go to <tt>stderr</tt>. Unless
	redirected, <tt>stderr</tt> is the console.</p>

	</blockquote>
	<h3><a href="#TOC">»</a><a name="algorithm">algorithm</a></h3>
	<blockquote>

	<p>Qhull implements the Quickhull algorithm for convex hull
	[Barber et al. <a href="#bar-dob96">'96</a>]. This algorithm
	combines the 2-d Quickhull algorithm with the <em>n</em>-d
	beneath-beyond algorithm [c.f., Preparata & Shamos <a
	href="#pre-sha85">'85</a>]. It is similar to the randomized
	algorithms of Clarkson and others [Clarkson & Shor <a
	href="#cla-sho89">'89</a>; Clarkson et al. <a href="#cla-meh93">'93</a>;
	Mulmuley <a href="#mulm94">'94</a>]. For a demonstration, see <a
	href="qh-eg.htm#how">How Qhull adds a point</a>. The main
	advantages of Quickhull are output sensitive performance (in
	terms of the number of extreme points), reduced space
	requirements, and floating-point error handling. </p>

	</blockquote>
	<h3><a href="#TOC">»</a><a name="structure">data structures</a></h3>
	<blockquote>

	<p>Qhull produces the following data structures for dimension <i>d</i>:
	</p>

	<ul>
	<li>A <em>coordinate</em> is a real number in floating point
	format. </li>
	<li>A <em>point</em> is an array of <i>d</i> coordinates.
	With option '<a href="qh-optq.htm#QJn">QJ</a>', the
	coordinates are joggled by a small amount. </li>
	<li>A <em>vertex</em> is an input point. </li>
	<li>A <em>hyperplane</em> is <i>d</i> normal coefficients and
	an offset. The length of the normal is one. The
	hyperplane defines a halfspace. If <i>V</i> is a normal, <i>b</i>
	is an offset, and <i>x</i> is a point inside the convex
	hull, then <i>Vx+b <0</i>.</li>
	<li>An <em>outer plane</em> is a positive
	offset from a hyperplane. When Qhull is done, all points
	will be below all outer planes.</li>
	<li>An <em>inner plane</em> is a negative
	offset from a hyperplane. When Qhull is done, all
	vertices will be above the corresponding inner planes.</li>
	<li>An <em>orientation</em> is either 'top' or 'bottom'. It is the
	topological equivalent of a hyperplane's geometric
	orientation. </li>
	<li>A <em>simplicial facet</em> is a set of
	<i>d</i> neighboring facets, a set of <i>d</i> vertices, a
	hyperplane equation, an inner plane, an outer plane, and
	an orientation. For example in 3-d, a simplicial facet is
	a triangle. </li>
	<li>A <em>centrum</em> is a point on a facet's hyperplane. A
	centrum is the average of a facet's vertices. Neighboring
	facets are <em>convex</em> if each centrum is below the
	neighbor facet's hyperplane. </li>
	<li>A <em>ridge</em> is a set of <i>d-1</i> vertices, two
	neighboring facets, and an orientation. For example in
	3-d, a ridge is a line segment. </li>
	<li>A <em>non-simplicial facet</em> is a set of ridges, a
	hyperplane equation, a centrum, an outer plane, and an
	inner plane. The ridges determine a set of neighboring
	facets, a set of vertices, and an orientation. Qhull
	produces a non-simplicial facet when it merges two facets
	together. For example, a cube has six non-simplicial
	facets. </li>
	</ul>

	<p>For examples, use option '<a href="qh-opto.htm#f">f</a>'. See <a
	href="../src/libqhull/qh-poly.htm">polyhedron operations</a> for further
	design documentation. </p>

	</blockquote>
	<h3><a href="#TOC">»</a>Imprecision in Qhull</h3>
	<blockquote>

	<p>See <a href="qh-impre.htm">Imprecision in Qhull</a> and <a href="qh-impre.htm#joggle">Merged facets or joggled input</a></p>

	</blockquote>
	<h3><a href="#TOC">»</a>Examples of Qhull</h3>
	<blockquote>

	<p>See <a href="qh-eg.htm">Examples of Qhull</a>. Most of these examples require <a href="#geomview">Geomview</a>.
	Some of the examples have <a
	href="http://www.geom.uiuc.edu/graphics/pix/Special_Topics/Computational_Geometry/welcome.html">pictures
	</a>.</p>

	</blockquote>
	</blockquote>
	<h2><a href="#TOC">»</a>Options for using Qhull </h2>
	<blockquote>

	<p>See <a href="qh-quick.htm#options">Options</a>.</p>

	</blockquote>
	<h2><a href="#TOC">»</a>Qhull internals </h2>
	<blockquote>

	<p>See <a href="qh-code.htm">Internals</a>.</p>

	</blockquote>
	<h2><a href="#TOC">»</a><a name="geomview">Geomview, Qhull's
	graphical viewer</a></h2>
	<blockquote>

	<p><a href="http://www.geomview.org">Geomview</a>
	is an interactive geometry viewing program.
	Geomview provides a good visualization of Qhull's 2-d and 3-d results.

	<p>Qhull includes <a href="qh-eg.htm">Examples of Qhull</a> that may be viewed with Geomview.

	<p>Geomview can help visulalize a 3-d Delaunay triangulation or the surface of a 4-d convex hull,
	Use option '<a href="qh-optq.htm#QVn">QVn</a>' to select the 3-D facets adjacent to a vertex.

	<p>You may use Geomview to create movies that animate your objects (c.f., <a href="http://www.geomview.org/FAQ/answers.shtml#mpeg">How can I create a video animation?</a>).
	Geomview helped create the <a href="http://www.geom.uiuc.edu/video/">mathematical videos</a> "Not Knot", "Outside In", and "The Shape of Space" from the Geometry Center.


	<h3><a href="#TOC">»</a><a name="geomview-install">Installing Geomview</a></h3>
	<blockquote>

	<p>Geomview is an <a href=http://sourceforge.net/projects/geomview>open source project</a>
	under SourceForge.

	<p>
	For build instructions see
	<a href="http://www.geomview.org/download/">Downloading Geomview</a>.
	Geomview builds under Linux, Unix, Macintosh OS X, and Windows.

	<p>Geomview has <a href="https://packages.debian.org/search?keywords=geomview">installable packages</a> for Debian and Ubuntu.
	The OS X build needs Xcode, an X11 SDK, and Lesstif or Motif.
	The Windows build uses Cygwin (see <a href="#geomview-win">Building Geomview</a> below for instructions).

	<p>If using Xforms (e.g., for Geomview's <a href="http://www.geomview.org/docs/html/Modules.html">External Modules</a>), install the 'libXpm-devel' package from cygwin and move the xforms directory into your geomview directory, e.g.,<br><tt>mv xforms-1.2.4 geomview-1.9.5/xforms</tt>

	<p>Geomview's <a href="http://www.geom.uiuc.edu/software/geomview/docs/NDview/manpagehelp.html">ndview<a/> provides multiple views into 4-d and higher objects.
	This module is out-of-date (<a href="http://sourceforge.net/p/geomview/mailman/message/2004152/">geomview-users: 4dview</a>).
	Download NDview-sgi.tar.Z at <a href="ftp://www.geom.uiuc.edu/pub/software/geomview/newpieces/sgi">newpieces</a> and 4dview at <a href="https://stuff.mit.edu/afs/sipb/project/3d/arch/sgi_62/lib/Geomview/modules/">Geomview/modules</a>.

	</blockquote>
	<h3><a href="#TOC">»</a><a name="geomview-use">Using Geomview</a></h3>
	<blockquote>

	<p>Use Geomview to view <a href="qh-eg.htm">Examples of Qhull</a>. You can spin the convex hull, fly a camera through its facets,
	and see how Qhull produces thick facets in response to round-off error.

	<p>Follow these instructions to view 'eg,01.cube' from Examples of Qhull
	<ol>
	<li>Launch an XTerm command shell
	<ul>
	<li>If needed, start the X terminal server, Use 'xinit' or 'startx' in /usr/X11R6/bin<br><tt>xinit -- -multiwindow -clipboard</tt><br><tt>startx</tt>
	<li>Start an XTerm command shell. In Windows, click the Cygwin/bash icon on your desktop.
	<li>Set the DISPLAY variable, e.g.,<br><tt>export DISPLAY=:0</tt><br><tt>export DISPLAY=:0 >>~/.bashenv</tt>
	</ul>
	<li>Use Qhull's <a href="qh-optg.htm">Geomview options</a> to create a geomview object
	<ul>
	<li><tt>rbox c D3 \| qconvex G >eg.01.cube</tt>
	<li>On windows, convert the output to Unix text format with 'd2u'<br><tt>rbox c D3 \| qconvex G \| d2u >eg.01.cube</tt><br><tt>d2u eg.*</tt>
	</ul>
	<li>Run Geomview
	<ul>
	<li>Start Geomview with your example<br><tt>./geomview eg.01.cube</tt>
	<li>Follow the instructions in <a href="http://www.geomview.org/docs/html/Tutorial.html">Gemoview Tutorial</a>
	<li>Geomview creates the <i>Geomview control panel</i> with Targets and External Module, the <i>Geomview toolbar</i> with buttons for controlling Geomview, and the <i>Geomview camera window</i> showing a cube.
	<li>Clear the camera window by selecting your object in the Targets list and 'Edit > Delete' or 'dd'
	<li>Load the <i>Geomview files panel</i>. Select 'Open' in the 'File' menu.
	<li>Set 'Filter' in the files panel to your example directory followed by '/' (e.g., '/usr/local/qhull-2015.1/eg/')
	<li>Click 'Filter' in the files panel to view your examples in the 'Files' list.
	<li>Load another example into the camera window by selecting it and clicking 'OK'.
	<li>Review the instructions for <a href="http://www.geomview.org/docs/html/Interaction.html">Interacting with Geomview</a>
	<li>When viewing multiple objects at once, you may want to turn off normalization. In the 'Inspect > Apperance' control panel, set 'Normalize' to 'None'.
	</ul>
	</ol>

	<p>Geomview defines GGL (a textual API for controlling Geomview) and OOGL (a textual file format for defining objects).
	<ul>
	<li>To control Geomview, you may use any program that reads and writes from stdin and stdout. For example, it could report Qhull's information about a vertex identified by a double-click 'pick' event.
	<li><a href="http://www.geomview.org/docs/html/GCL.html">GCL</a> command language for controlling Geomview
	<li><a href="http://www.geomview.org/docs/html/OOGL-File-Formats.html">OOGL</a> file format for defining objects (<a href="http://www.geomview.org/docs/oogltour.html">tutorial</a>).
	<li><a href="http://www.geomview.org/docs/html/Modules.html">External Modules</a> for interacting with Geomview via GCL
	<li>Interact with your objects via <a href="http://www.geomview.org/docs/html/pick.html">pick</a> commands in response to right-mouse double clicks. Enable pick events with the <a href="http://www.geomview.org/docs/html/interest.html">interest</a> command.
	</ul>

	</blockquote>
	<h3><a href="#TOC">»</a><a name="geomview-win">Building Geomview for Windows</a></h3>
	<blockquote>

	<p>Compile Geomview under Cygwin. For detailed instructions, see
	<a href="http://www.ee.surrey.ac.uk/Personal/L.Wood/software/SaVi/building-under-Windows/"
	>Building Savi and Geomview under Windows</a>. These instructions are somewhat out-of-date. Updated
	instructions follow.

	<p>How to compile Geomview under Cygwin (October 2015)</p>
	<ol>
	<li>Install <a href="http://cygwin.com/">Cygwin</a> as follows.
	For additional guidance, see Cygwin's <a href="https://cygwin.com/install.html">Installing and Updating Cygwin Packages</a>
	and <a href="http://www.qhull.org/road/road-faq/xml/cmdline.xml#setup-cygwin">Setup cygwin</a>.
	<ul>
	<li>Launch the cygwin installer.
	<li>Select a mirror from <a href="http://cygwin.com/mirrors.html">Cygwin mirrors</a> (e.g., http://mirrors.kernel.org/sourceware/cygwin/ in California).
	<li>Select the packages to install. Besides the cygwin packages listed in the Savi/Windows instructions consider adding
	<ul>
	<li><b>Default</b> -- libXm-devel (required for /usr/include/Xm/Xm.h)
	<li><b>Devel</b> -- bashdb, gcc-core (in place of gcc), gdb
	<li><b>Lib</b> -- libGL-devel, libGLU1 (required, obsolete), libGLU-devel (required, obsolete), libjpeg-devel(XForms), libXext-devel (required), libXpm-devel (Xforms)
	libGL and lib
	<li><b>Math</b> -- bc
	<li><b>Net</b> -- autossh, inetutils, openssh
	<li><b>System</b> -- chere
	<li><b>Utils</b> -- dos2unix (required for qhull), keychain
	<li>If installing perl, ActiveState Perl may be a better choice than cygwin's perl. Perl is not used by Geomview or Qhull.
	<li><a href="https://cygwin.com/cgi-bin2/package-grep.cgi">Cygwin Package Search</a> -- Search for cygwin programs and packages
	</ul>
	<li>Click 'Next' to download and install the packages.
	<li>If the download is incomplete, try again.
	<li>If you try again after a successful install, cygwin will uninstall and reinstall all modules..
	<li>Click on the 'Cywin Terminal' icon on the Desktop. It sets up a user directory in /home from /etc/skel/...
	<li>Mount your disk drives<br>mount c: /c # Ignore the warning /c does not exist
	<li>Consider adding 'cygwin\bin' to '<tt>Control Panel > System > Advanced > Environment > PATH</tt>'. If so, cygwin commands such as 'ls' may be used from the Windows command shell.
	</ul>
	<li>Consider installing the <a href="http://www.qhull.org/bash/doc/road-bash.html">Road Bash</a> scripts (/etc/road-*) from <a href="http://www.qhull.org/road/">Road</a>.
	They define aliases and functions for Unix command shells (Unix, Linux, Mac OS X, Windows),
	<ul>
	<li>Download Road Bash and unzip the downloaded file
	<li>Copy .../bash/etc/road-* to the Cywin /etc directory (by default, C:\cygwin\etc).
	<li>Using the cygwin terminal, convert the road scripts to Unix format<br>d2u /etc/road-*
	<li>Try it<br>source /etc/road-home.bashrc
	<li>Install it<br>cp /etc/road-home.bashrc ~/.bashrc
	</ul>
	<li>Launch the X terminal server from '<tt>Start > All programs > Cygwin-X > Xwin Server</tt>'. Alternatively, run 'startx'
	<li>Launch an XTerm shell
	<ul>
	<li>Right click the Cywin icon on the system tray in the Windows taskbar.
	<li>Select '<tt>System Tools > XTerm</tt>'
	</ul>
	<li>Download and extract Geomview -- <a href="http://www.geomview.org/download/">Downloading Geomview</a>
	<li>Compile Geomview
	<ul>
	<li>./configure
	<li>make
	</ul>
	<li>If './configure' fails, check 'config.log' at the failing step. Look carefully for missing libraries, etc. The <a href="http://www.geomview.org/FAQ/answers.shtml">Geomview FAQ</a> contains suggestions (e.g., "configure claims it can't find OpenGl").
	<li>If 'make' fails, read the output carefully for error messages. Usually it is a missing include file or package. Locate and install the missing cygwin packages
	(<a href="https://cygwin.com/cgi-bin2/package-grep.cgi">Cygwin Package Search</a>).
	</ol>

	</blockquote>
	</blockquote>
	<h2><a href="#TOC">»</a><a name="bugs">What to do if something
	goes wrong</a></h2>
	<blockquote>

	<p>Please report bugs to <a href=mailto:qhull_bug@qhull.org>qhull_bug@qhull.org</a>
	</a>. Please report if Qhull crashes. Please report if Qhull
	generates an "internal error". Please report if Qhull
	produces a poor approximate hull in 2-d, 3-d or 4-d. Please
	report documentation errors. Please report missing or incorrect
	links.</p>

	<p>If you do not understand something, try a small example. The <a
	href="rbox.htm">rbox</a> program is an easy way to generate
	test cases. The <a href="#geomview">Geomview</a> program helps to
	visualize the output from Qhull.</p>

	<p>If Qhull does not compile, it is due to an incompatibility
	between your system and ours. The first thing to check is that
	your compiler is ANSI standard. Qhull produces a compiler error
	if __STDC__ is not defined. You may need to set a flag (e.g.,
	'-A' or '-ansi').</p>

	<p>If Qhull compiles but crashes on the test case (rbox D4),
	there's still incompatibility between your system and ours.
	Sometimes it is due to memory management. This can be turned off
	with qh_NOmem in mem.h. Please let us know if you figure out how
	to fix these problems. </p>

	<p>If you doubt the output from Qhull, add option '<a
	href="qh-optt.htm#Tv">Tv</a>'. It checks that every point is
	inside the outer planes of the convex hull. It checks that every
	facet is convex with its neighbors. It checks the topology of the
	convex hull.</p>

	<p>Qhull should work on all inputs. It may report precision
	errors if you turn off merged facets with option '<a
	href="qh-optq.htm#Q0">Q0</a>'. This can get as bad as facets with
	flipped orientation or two facets with the same vertices. You'll
	get a long help message if you run into such a case. They are
	easy to generate with <tt>rbox</tt>.</p>

	<p>If you do find a problem, try to simplify it before reporting
	the error. Try different size inputs to locate the smallest one
	that causes an error. You're welcome to hunt through the code
	using the execution trace ('<a href="qh-optt.htm#Tn">T4</a>') as
	a guide. This is especially true if you're incorporating Qhull
	into your own program. </p>

	<p>When you report an error, please attach a data set to the end
	of your message. Include the options that you used with Qhull,
	the results of option '<a href="qh-optf.htm#FO">FO</a>', and any
	messages generated by Qhull. This allows me to see the error for
	myself. Qhull is maintained part-time. </p>

	</blockquote>
	<h2><a href="#TOC">»</a><a name="email">Email</a></h2>
	<blockquote>

	<p>Please send correspondence to Brad Barber at <a href=mailto:qhull@qhull.org>qhull@qhull.org</a>
	and report bugs to <a href=mailto:qhull_bug@qhull.org>qhull_bug@qhull.org</a>
	</a>. Let me know how you use Qhull. If you mention it in a
	paper, please send a reference and abstract.</p>

	<p>If you would like to get Qhull announcements (e.g., a new
	version) and news (any bugs that get fixed, etc.), let us know
	and we will add you to our mailing list. For Internet news about geometric algorithms
	and convex hulls, look at comp.graphics.algorithms and
	sci.math.num-analysis. For Qhull news look at <a
	href="http://www.qhull.org/news">qhull-news.html</a>.</p>

	</blockquote>
	<h2><a href="#TOC">»</a><a name="authors">Authors</a></h2>
	<blockquote>

	<pre>
	C. Bradford Barber Hannu Huhdanpaa
	bradb@shore.net hannu@qhull.org
	</pre>

	</blockquote>
	<h2><a href="#TOC">»</a><a name="acknowledge">Acknowledgments</a></h2>
	<blockquote>

	<p>A special thanks to David Dobkin for his guidance. A special
	thanks to Albert Marden, Victor Milenkovic, the Geometry Center,
	and Harvard University for supporting this work.</p>

	<p>A special thanks to Mark Phillips, Robert Miner, and Stuart Levy for running the Geometry
	Center web site long after the Geometry Center closed.
	Stuart moved the web site to the University of Illinois at Champaign-Urbana.
	Mark and Robert are founders of <a href=http://www.geomtech.com>Geometry Technologies</a>.
	Mark, Stuart, and Tamara Munzner are the original authors of <a href=http://www.geomview.org>Geomview</a>.

	<p>A special thanks to <a href="http://www.endocardial.com/">Endocardial
	Solutions, Inc.</a> of St. Paul, Minnesota for their support of the
	internal documentation (<a href=../src/libqhull/index.htm>src/libqhull/index.htm</a>). They use Qhull to build 3-d models of
	heart chambers.</p>

	<p>Qhull 1.0 and 2.0 were developed under National Science Foundation
	grants NSF/DMS-8920161 and NSF-CCR-91-15793 750-7504. If you find
	it useful, please let us know.</p>

	<p>The Geometry Center was supported by grant DMS-8920161 from the
	National Science Foundation, by grant DOE/DE-FG02-92ER25137 from
	the Department of Energy, by the University of Minnesota, and by
	Minnesota Technology, Inc.</p>

	</blockquote>
	<h2><a href="#TOC">»</a><a name="ref">References</a></h2>
	<blockquote>

	<p><a name="aure91">Aurenhammer</a>, F., "Voronoi diagrams
	-- A survey of a fundamental geometric data structure," <i>ACM
	Computing Surveys</i>, 1991, 23:345-405. </p>

	<p><a name="bar-dob96">Barber</a>, C. B., D.P. Dobkin, and H.T.
	Huhdanpaa, "The Quickhull Algorithm for Convex Hulls," <i>ACM
	Transactions on Mathematical Software</i>, 22(4):469-483, Dec 1996, www.qhull.org
	[<a
	href="http://portal.acm.org/citation.cfm?doid=235815.235821">http://portal.acm.org</a>;
	<a href="http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.117.405">http://citeseerx.ist.psu.edu</a>].
	</p>

	<p><a name="cla-sho89">Clarkson</a>, K.L. and P.W. Shor,
	"Applications of random sampling in computational geometry,
	II", <i>Discrete Computational Geometry</i>, 4:387-421, 1989</p>

	<p><a name="cla-meh93">Clarkson</a>, K.L., K. Mehlhorn, and R.
	Seidel, "Four results on randomized incremental
	construction," <em>Computational Geometry: Theory and
	Applications</em>, vol. 3, p. 185-211, 1993.</p>

	<p><a name="devi01">Devillers</a>, et. al.,
	"Walking in a triangulation," <i>ACM Symposium on
	Computational Geometry</i>, June 3-5,2001, Medford MA.

	<p><a name="dob-kir90">Dobkin</a>, D.P. and D.G. Kirkpatrick,
	"Determining the separation of preprocessed polyhedra--a
	unified approach," in <i>Proc. 17th Inter. Colloq. Automata
	Lang. Program.</i>, in <i>Lecture Notes in Computer Science</i>,
	Springer-Verlag, 443:400-413, 1990. </p>

	<p><a name="edel01">Edelsbrunner</a>, H, <i>Geometry and Topology for Mesh Generation</i>,
	Cambridge University Press, 2001.

	<p><a name=gart99>Gartner, B.</a>, "Fast and robust smallest enclosing balls", <i>Algorithms - ESA '99</i>, LNCS 1643.

	<p><a name=golub83>Golub, G.H. and van Loan, C.F.</a>, <i>Matric Computations</i>, Baltimore, Maryland, USA: John Hopkins Press, 1983

	<p><a name="fort93">Fortune, S.</a>, "Computational
	geometry," in R. Martin, editor, <i>Directions in Geometric
	Computation</i>, Information Geometers, 47 Stockers Avenue,
	Winchester, SO22 5LB, UK, ISBN 1-874728-02-X, 1993.</p>

	<p><a name="mile93">Milenkovic, V.</a>, "Robust polygon
	modeling," Computer-Aided Design, vol. 25, p. 546-566,
	September 1993. </p>

	<p><a name="muck96">Mucke</a>, E.P., I. Saias, B. Zhu, <i>Fast
	randomized point location without preprocessing in Two- and
	Three-dimensional Delaunay Triangulations</i>, ACM Symposium on
	Computational Geometry, p. 274-283, 1996 [<a
	href="http://www.geom.uiuc.edu/software/cglist/GeomDir/">GeomDir</a>].
	</p>

	<p><a name="mulm94">Mulmuley</a>, K., <i>Computational Geometry,
	An Introduction Through Randomized Algorithms</i>, Prentice-Hall,
	NJ, 1994.</p>

	<p><a name="orou94">O'Rourke</a>, J., <i>Computational Geometry
	in C</i>, Cambridge University Press, 1994.</p>

	<p><a name="pre-sha85">Preparata</a>, F. and M. Shamos, <i>Computational
	Geometry</i>, Springer-Verlag, New York, 1985.</p>

	</blockquote>
	<!-- Navigation links -->
	<hr>

	<p><b>Up:</b> <a
	href="http://www.qhull.org">Home page</a> for Qhull<br>
	<b>Up:</b><a
	href="http://www.qhull.org/news">News</a> about Qhull<br>
	<b>Up:</b> <a href="http://www.qhull.org/html/qh-faq.htm">FAQ</a> about Qhull<br>
	<b>To:</b> <a href="#TOC">Qhull manual</a>: Table of Contents<br>
	<b>To:</b> <a href="qh-quick.htm#programs">Programs</a>
	<a href="qh-quick.htm#options">Options</a>
	<a href="qh-opto.htm#output">Output</a>
	<a href="qh-optf.htm#format">Formats</a>
	<a href="qh-optg.htm#geomview">Geomview</a>
	<a href="qh-optp.htm#print">Print</a>
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	<a href="qh-optc.htm#prec">Precision</a>
	<a href="qh-optt.htm#trace">Trace</a><br>
	<b>Dn:</b> <a href="qh-impre.htm">Imprecision in Qhull</a><br>
	<b>Dn:</b> <a href="qh-eg.htm">Description of Qhull examples</a><br>
	<b>Dn:</b> <a href="qh-code.htm">Qhull internals</a><br>
	<b>Dn:</b> <a href="../src/libqhull/index.htm">Qhull functions, macros, and data
	structures</a>
	<!-- GC common information -->
	<hr>

	<p><a href="http://www.geom.uiuc.edu/"><img src="qh--geom.gif"
	align="middle" width="40" height="40"></a><i>The Geometry Center
	Home Page </i></p>

	<p>Comments to: <a href=mailto:qhull@qhull.org>qhull@qhull.org</a>
	</a><br>
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